To conduct a rigidly controlled metabolic study on trace elements of six young normal female graduate students in a special metabolic facility. They will be fed a constant formula type diet containing all known essential nutrients. Analysis of all losses will be made including urinary, fecal, skin, and menstrual losses. The subjects will receive in random order two months of no steroidal agent, one month of a sequential type oral contraceptive, and one month of a combined estrogen-progesterone agent. In addition to studies of trace elements, the effects of contraceptives will be evaluated on calcium, magnesium, and nitrogen balances, particularly in regard to cyclic variations. Blood samples will be obtained and analyzed three times per menstrual cycle. Basal metabolic rates and requirements to perform a fixed amount of work will be determined and body weight variations will be observed.